ABSTRACT: Objective: The
standard practice in fractionated radiation of using of visual alignment of
tattoos with weekly portal imaging for radiation setup can miss setup errors. We
previously reported on the feasibility of using an automated infrared-guided
positioning system (iGPS) for daily radiation setup. In this study, we
prospectively evaluate whether use of iGPS can improve daily setup errors for
patients with thoracic malignancies. Methods: Multiple external infrared
markers were placed on patients undergoing thoracic radiation at the time of
simulation. Patients were immobilized using vacuum immobilization bag and
wing-board. Patients were aligned for treatment using only the iGPS system. Daily
portal images were then taken, and shifts in patient position were recorded. Differences
between isocenter position using iGPS versus daily portal imaging were
calculated. Results: Data were collected for 698 treatment sessions for
27 patients. We found that in 94.0%, 96.4%, and 93.7% of treatment sessions,
isocenter position differed between iGPS and daily portal imaging by ≤5 mm in the left/right(L/R), anterior/posterior(A/P),
and superior/inferior(S/I) directions, respectively. Isocenter position
differed by 5 - 10 mm in
5.7% (L/R), 3.6% (A/P), and 5.9% (S/I) of treatment sessions, and by >10 mm in 0.3% (L/R), 0.0% (A/P), and 0.4% (S/I) of
treatment sessions. Three-dimensional shifts were also calculated, with
differences in isocenter position as follows: 94.9% ≤5 mm, 5.1% 5 - 10 mm, and
0.2% >10 mm. This
compares favorably to our prior studies. Discussion: Daily treatment
setup using an infrared-guided patient positioning system, correlates well with
daily portal imaging and may help to improve daily treatment setup for patients
with thoracic malignancies.